1. Field of the Invention
The present invention relates to arrangements and methods for the non-contact sealing of gaps in fluid-flow machines, in particular in gas turbines.
2. Discussion of Background
The design of fluid-flow machines requires end-to-end mounting of components which are stationary and/or moving relative to one another. For functional reasons, one or more gaps, over which a primary-fluid flow flows in the flow duct of the fluid-flow machine, often remain between these components. Penetration of the primary fluid into these gaps is associated with this. Specifically in the hot-gas part of a gas turbine, penetration of the hot primary fluid into component gaps must be avoided at all costs on account of the high temperatures of the primary fluid, which are often even higher than the maximum permissible material temperatures. Hot primary fluid which nonetheless penetrates into the gaps, as a consequence of the heat exchange with the components adjacent to the gap, may therefore lead to inadmissibly high temperatures of these components. This in turn is the cause of component damage, in particular in the form of component cracks or an at least marked reduction in the service life of these components. In addition, gaps lead to flow leakages of the primary-fluid flow and thus to losses in the efficiency of gas turbines.
These gaps have hitherto been sealed against the primary fluid by means of mechanical seals such as, for example, seal plates and seal strips, bellows and spring-loaded seals or even by means of arrangements for fluid-dynamic sealing.
Mechanical seals, on account of their contacting operating principle, are subjected to abrasive wear and consequently have only a limited service life.
In the hitherto known arrangements for fluid-dynamic sealing, the aim is to block the gap by means of a unidirectional displacement flow. This displacement flow seals the gap against the primary fluid either by means of a continuous secondary-fluid flow discharged out of the gap into the primary-fluid flow, as described, for example, in CH 529 914, or by means of a secondary-fluid film covering the gap.
In the first case, a secondary fluid of increased backpressure is admitted to the gap at the gap opening remote from the primary flow. The higher pressure of the secondary fluid produces a unidirectional gap flow from the secondary-fluid-side reservoir into the primary flow.
In the second known method for the purpose of the fluid-dynamic sealing of a gap, a unidirectional secondary-fluid flow having a velocity component at right angles to the longitudinal direction of the gap is produced in the form of a secondary-fluid film covering the gap. As a result of the displacement effect of the secondary fluid, a fluid-mechanical separation of the primary fluid from a tertiary fluid located in the gap is thereby achieved. In this case, the tertiary fluid originates from a tertiary-fluid reservoir and flows into the gap via that opening of the gap which is remote from the primary flow. If this does not involve a gap between two components but rather a recess in one component, this recess has a closed component contour. There is therefore no connection to a reservoir of the tertiary fluid, provided there is no additional arrangement, such as, for example, a supply conduit. For the purpose of simplification, that volume of the recess which remains as dead volume of the recess on that side of the vortex flow which is remote from the primary flow is likewise designated below as tertiary-fluid-side gap portion.
However, both arrangements for the fluid-dynamic sealing require a comparatively high mass flow rate of the secondary fluid used for the sealing. In a use of secondary fluid branched off from the compressor region, which is a conventional use in practice, these methods also often have only limited effectiveness, in particular in the turbine inlet region. As a cause of this, for example a local build-up of the flow in front of the vanes of the inlet guide disk of the turbine may lead to a local increase in the static pressure of the primary-fluid flow. During a pressure loss of the primary flow in the combustion chamber, which loss is only slight as a rule, the local static pressure of the primary flow, when flowing over a gap, may be higher in the turbine inlet region than the pressure of the secondary fluid extracted directly in front of the combustion chamber and supplied to the turbine. As a result of this pressure gradient, a local inflow of the hot primary fluid occurs in at least sections of the gap.
Thermally or mechanically induced component expansions and the resulting changes in the geometric dimensions of the gaps as well as displacements of the components relative to one another in the longitudinal direction of the gap considerably increase the demands imposed on the seals used. Thermally induced changes in the component geometry occur in particular in the hot-gas part of a gas turbine. The result is frequent malfunctions of both the mechanical seals and the arrangements for the fluid-dynamic sealing. In addition, the service life of the mechanical seals is further reduced to a significant degree.
Described in Patent Specifications GB 855 040 and U.S. Pat. No. 3,645,544 are sealing arrangements in which, in order to seal a gap against a primary fluid, a secondary fluid is supplied into the gap in such a way that a vortex system forms in the gap. However, the sealing arrangements described can in each case be used only for gaps between two components where the components rotate relative to one another and the gaps in each case extend over the entire periphery.